Insulating glass units (IGU's) have been used in windows to reduce heat loss from building interiors during cold weather or to reduce heat gain in building interiors during hot weather. IGU's are typically formed by a spacer assembly that is sandwiched between glass lites. The spacer assembly usually comprises a frame structure that extends peripherally around the unit, an adhesive material that adheres the glass lites to opposite sides of the frame structure, and desiccant in an interior region of the frame structure for absorbing atmospheric moisture within the IGU. The glass lites are flush with or extend slightly outwardly from the spacer assembly. The adhesive is disposed on opposite outer sides of the frame structure about the frame structure periphery, so that the spacer is hermetically sealed to the glass lites. An outer frame surface that defines the spacer periphery may also be coated with sealant, which increases the rigidity of the frame and acts as a moisture barrier.
One type of spacer construction employs a “U” or rectangular shaped, roll formed aluminum or steel element that Is bent and connected at its two ends to form a square or rectangular spacer frame. Opposite sides of the frame are covered with an adhesive (e.g., a hot melt material) for securing the frame to the glass lites. The adhesive provides a barrier between atmospheric air and the IGU interior which blocks entry of atmospheric water vapor. Desiccant is deposited in an interior region of the U-shaped frame element. The desiccant is in communication with the air trapped in the IGU interior and removes any entrapped water vapor and thus impedes water vapor from condensing within the IGU. After the water vapor entrapped in the IGU is removed, internal condensation only occurs when the seal between the spacer assembly and the glass lights fails or the glass lights are cracked.
Prior art systems for applying adhesive to outer surfaces of a spacer and desiccant to an inner region of the spacer are pressure-based systems. Desiccant or adhesive under pressure is supplied from a bulk supply, such as a 55-gallon drum by a piston driven pump. A hose delivers the desiccant or adhesive in response to actuation of the piston driven pump to an inlet of a compensator. The compensator allows a user to select a desired pressure that will be provided at the outlet of the compensator. When the pressure at the outlet of the compensator is less than the selected pressure, the desiccant or adhesive material under pressure supplied to the inlet of the compensator causes the piston to move from a “closed” position to an “open” position. Movement of the compensator piston to the “open” position allows the material under pressure supplied to the compensator inlet to flow toward the outlet until the pressure at the outlet reaches the selected pressure. When the pressure at the outlet reaches or slightly exceeds the selected pressure, the material under pressure at the outlet of the compensator forces the piston back to the “closed” position, stopping material flow from the compensator inlet to the outlet.
Prior art systems include needle valves that dispense the material into contact with spacer frames. The needle valves are adjustable by the user to control the flow rate of the desiccant or adhesive. The flow of the desiccant or adhesive material is determined by the orifice size of the needle valve and the viscosity and pressure of the material. The pressure of the adhesive or desiccant material is dependent on several variables, including viscosity, temperature, nozzle size, and batch to batch variations of the dispensed material. Because so many variables are involved, the amount of desiccant or adhesive dispensed is subject to a fairly wide fluctuation due to pressure changes that are attributable to various factors mentioned above.
Pressure-based application systems require the operator to constantly adjust for flow. Often, an excessive amount of material is dispensed to ensure that under all conditions an adequate amount of material is applied to the spacer frame. If the dispensing system is down for more than a few minutes, the system has to be purged due to an increased viscosity of the desiccant or adhesive that has cooled. The increased viscosity of the material that has been allowed to cool makes it difficult to pass the material through the nozzle and flow material through the system.
Multipane window units have been proposed that do not include an insulating glass unit. The glass panes of these multipane window units are attached directly to a sash assembly. Sash assemblies generally have a closed perimeter that may define a square, rectangle, circle, oval or other shape. Application of sealant and/or desiccant to a sash assembly is difficult because the sealant and/or desiccant is applied along a nonlinear application path defined by the sash perimeter. In the case of rectangular sash assemblies, the application path includes right angles that may require the sealant and/or desiccant to be applied at variable rates.
One problem, identified by the inventor of the present application, with multipane window units that do not include an insulating glass unit is that sash assemblies are often made from a porous material. As a result, moisture may pass through the sash assembly into the region between the glass panes. This moisture will result in condensation inside the multipane window unit.
The prior art pressure based adhesive and/or desiccant application systems are not configured to apply adhesive and/or desiccant along a non-linear path or apply adhesive and/or desiccant at variable rates. In addition, prior art sash assemblies do not include a film or coating that prevents moisture from entering the multipane window unit.